When I adjusted mine (stock), I went round a mates as he was the only person I could think of who might have a C-spanner.
Unfortunately, the ones he had were no good as the shape of them meant that bits of bike kept getting in the way, so we used a torx driver that he didn't mind sacrificing in an adaptor on a socket wrench, this did it fine.
This is also the main reason I have yet to adjust them back as I haven't been round there since
The proper tool would probably be better though
